The continuous cell lines that are available for investigation of renal epithelial cell biology were intially grown for other purposes, and do not express many of the important transport systems of the various parts of the nephron. Therefore, we are attempting to establish new cell lines from defined tubule segments. Our strategy is to dissect fragments of each kind of renal tubule, grow them in culture, and screen the primary cultures as well as any continuous lines for transport function. Previously, we had succeeded in growing primary cultures from single nepbron segments, but had not succeeded in growing the cells continuously. In the past year we have developed techniques for continuous culuture. The single most important advance has been the use of sheep amninons as a support for growing the cells. Cells from rabbit medullary thick ascending limbs have now been carried through up to 10 passages over several months, using this method. Once the lines are established in this manner, it also becomes possible to grow them continuously on colagencoated plastic dishes, which was not successful before. The thick ascending limb cells have expressed differentiated function up to the fourth passage, measured as a characteristic transpithelial vortage. We now will attempt to culture other segments from rabbit and segments from mice and rats as well, using these techniques. Also, we are beginning to study the morphology of the cultures on aminos in collaboration with Drs. Timothy Triche and Alice Algren of NCI, LP and are studying the effects of agents and conditions found to affect growth and differentiation in other systems.